Electrical circuit



July 4, 1939. G GUANELLA 2 164AQ2 ELECTRICAL CIRCUIT Filed Feb. 17, 19382 Sheejas-Sheet 2 INVBT-JTOR. gusfav FSILZLGMQZZQ BY ATTORNEY,

Patented July 4, 1939 UNITED STATES ELECTRICAL CIRCUIT Gustav Guanciia,Zurich, Switaerland, aaaignor to Radio Patents Corporation, New York, N.1.. a corporation of New York Application February 17, 1938, Serial No.190,940 In swltlerland March 10, 1937 iiCla-ims.

The present invention relates to phase or polarity reversingarrangements and a method of operating the same for use in either director alternating current systems.

An object of the invention is the provision of a phase reversing systemwhich avoids the use of transformers and the distortions and otherdefects connected therew th.

Another object is the provision of a phase or polarity reversing systemwhich is equally efiective for both high and low frequencies as well asdirect currents.

A further object is to provide a system for and a method ofsimultaneously reversing the phases by 180 of a large number of electriccurrents or potentials of different frequencies such as the frequencycomponents of a current or potential signal Wave.

Still another object is the provision of a phase reversing systemembodying amplifying valves wherein the phase and amplitude of thereversed potential or current is substantially independent of theamplification and other constants of the valve and circuits used.

A further object is the provision of a push-pull modulating systemconstructed without the use of transformers or inductance coils.

Another object is the provision of a novel pushpull modulating systemdesigned and operating without the use of transformers or choke coils.

Still another object is to provide a system for producing the sum anddifference of alternating currents or potentials of like or diiferentfrequencies.

' The above and further objects and advantages of the invention willbecome more apparent from the following detailed description taken inreference with the accompanying drawings forming part of thisspecification and wherein;

Figures 1 and 2 illustrate diagrammatically phase reversing devicesknown in the art,

Figure 3 'shows a phase reversing network of known type employing anelectron valve as a reversing element,

Figures 4 and 5 illustrate an improved phase or polarity reversingsystem employing an electron valve as a reversing element in accordancewith the invention,

Figure 6 illustrates the employment of a phase reversing networkaccording to the invention in a push-pull amplifier,

Figure 7 illustrates a push-pull system with a phase reversing system ofthe type according to the invention employing a multi-purpose electronvalve,

Figure 8 illustrates a further embodiment of the invention as applied toa push-pull modulating circuit arrangement designed without the use oftransformers.

Like reference numerals identify like parts 5 throughout the differentviews of the drawings.

It is a common requirement in the electrical and radio arts to rotatethe phase of an alternating or oscillating current or of a plurality ofsuch currents or potentials by 180. Various cir- 10 cults for thisgeneral purpose are known. For example, there is shown in Figure 1 aknown four terminal network comprising input terminals 41 and b andoutput terminals c and d of which terminals b and d are common. P is aphase reversing device by which the sign of the voltage in appliedbetween terminals 11 and b is reversed, so that if terminal a is at apotential +u1 with respect to terminal 1;, terminal 0 will be at anopposite potential uz=ui with respect to terminal d. The phase reversingarrangement at P might be a center tapped choke coil in series between aand c with its center tapping connected to the common terminals b and d.In some cases, especially where the input voltage at a--b is analternating voltage of known predetermined frequency, P could be anetwork of the resonant type with inductance, capacity and resistance.

The problem of phase reversal also arises where a voltage which isvarying in relation to earth or to some other fixed datum potential isrequired to be transformed into a symmetrical voltage, that is to say,where, referring to the accompanying Figure 2, one input terminal avaries in potential above a second, earthed or fixed potential inputterminal b (voltage a) and it is required that two output terminals 0and e shall vary equally and opp sitely (voltage +u and u) with respectto a point d which is at earth or said fixed datum potential.

The accompanying Figure 3 shows within the chain rectangle P a knownphase reversing arrangement which can be used for the device P of Figure2. An example of a case requiring a network of the type of Figures 2 and3 is where it is required to feed from an ordinary single valvethermionic valve amplifier into a push-pull valve amplifier stage. Inthis case, output voltage of the single valve or straight amplifier isapplied to terminal a, while the control grids of the two valves in thepush-pull stage are connected, respectively, to the terminals c and e'of Figure 2.

It is common practice of course to couple a straight stage to apush-pull stage by means of the usual push-pull input transformer whichhas a secondary winding with an earthed center tap. but the use of thesetransformers involves practical disadvantages such as cost and liabilityto distortion and Figure 3 shows one known arrangement which has beensuggested in order to avoid the use of transformers. In the latter, thephase reversal network includes a valve l comprising a cathode H, gridl2 and anode or plate l3. The control-grid I2 is connected to a tap on avoltage divider resistance M which is connected between terminals (1 and22. Item I5 is an anode or load impedance connected across the anode andcathode in series with a high tension supply source l6, and I1 is acoupling condenser connected between the anode l3 and output terminal 0.If a voltage in is impressed between a and b the voltage on the gridwill be wherein R represents the entire resistance H and r the tappedportion thereof connected across the grid-cathode path of the valve. Ifn is the amplification of the valve, the output alternating voltage aswill be By suitable choise of r it is therefore always possible to makeuz (the voltage between 0 and (1) equal to 11.1.

A disadvantage of this known circuit according to Figure 3 is the factthat small variations of valve amplification, such as produced byvariations in the operating voltages or as a result of changing thevalves have a large effect on the amplitude of uz with respect to theinput voltage in. For this reason the production and maintenance ofsymmetry is in practice difllcult and the present invention seeks toovercome this defect.

Referring to Figure 4, there is shown a phase rotating arrangementaccording to the invention comprising a potential divider consisting oftwo series portions l9 and 20 connected between the terminals a and cwith the junction point a; between them connected to the grid H of theamplifier valve l0 whose cathode is connected to the earthed or fixedpotential terminal b. Item II is a blocking condenser to block the anodepotential source Hi from the grid l2. If the instantaneous voltagebetween a and b. and impressed on the terminal a is m the voltage as atterminal 0 and between 0 and d is equal to m as will be seen later.

If u; is the voltage at the junction between 19 and 20 impressed uponthe grid l2, then, assuming the voltage divider l9 and 20 to be ofsufliciently high impedance and the anode resistance IS" in serieswiththe anode source l6 and the loading impedance connected to theterminals c and 11 also to be suificiently high, the output voltage u:at the terminal 0 will be equal to -u n where n is the amplification ofthe valve and the voltage 11; will be equal to I9 and 20, respectively.From this it follows that l assuming both impedance I5 and theloadimsufficiently large R1 will be only slightly different from R2. Itis'possible to write the above formula with a high degree ofapproximation in the simpler form From this it can be seen that theamplitude of the output voltage in will, if there is a sufficiently highamplification, only depend to a very slight extent on the fluctuationsin n. The elements It! and 20 need not be pure ohmic resistances but ifthey are reactive impedances such as inductances or capacities the phaseshifts introduced thereby should be equal. For example, Figure 5 is thesame as Figure 4 except that a choke with a tapped portion 2i and 2|replaces the resistive divider I9, 20 of Figure 4.

It may be noted that the output voltage uz is in general ofsubstantially the same amplitude as the voltage in impressed on theinput terminals a, b, no perceptible amplification occurringnotwithstanding any amplification factor valve Ill. This function of theinventive circuit may be further explained by the fact that asubstantial amount of output energy is fed back from the plate l3 to thegrid l2 through the condenser l1 and resistance 20 in inverse phaserelation to the input energy thereby reducing the amplification of thevalve. Thus while utilizing the eifect of phasereversal between the gridand plate potential of a vacuum valve the invention provides a means forsubstantially suppressing undesired amplification by inverse feedbackthereby avoiding the disadvantages and drawbacks incident thereto aspointed out hereinabove.

In practice, in order to facilitate adjustment it is advisable to makeone or both the impedances I 9, 2B or 2|, 2| variable within limits. Forexample, one of these impedances can be consti tuted by a fixedrelatively large impedance, such as a fixed resistance, fixed condenseror inductance in series with a relatively small variable supplementaryimpedance of the same character. Again the voltage divider can beconstituted by two fixed impedances connected in series by a voltagedivider element of low impedance which has a variable tappingconstituting the point u Since in general it is required that IS and 20,2| and 2| be impedances of relatively high absolute values, it ispossible thatequalization may, in practice, be disturbed by thegrid-anode capacity of the amplifier valve In which capacity is inparallel with 20 or 2| only. If difficulty occurs due to this it may beremedied by connecting a suitable capacity in parallel with impedance I9or 2| as shown at 22 in Figures 4 and 5, respectively.

The blocking condenser H in Figure 4 can be replaced by a voltage source23 as shown in v of direct current voltages, in which latter case a highohmic impedance potential divider I9, 20 is preferably used as shown inFigure 4.

Figure 6 shows an arrangement in accordance with the invention employedto couple a straight" amplifier stage to a push-pull amplifier stage. Inthis figure, item is a straight amplifier valve, 26 and 21 are its anoderesistance and anode potential source, respectively. Items 28 and 29 arethe push-pull valves, 30 is a coupling condenser, ii is the phasereversing valve, and 32 and 33 its anode resistance and anode potentialsource, respectively. Item 34 is a blocking condenser, item 35 is a gridleak resistance for valve 3|, and 36 is a self-bias resistance which isshunted by a condenser 31 and is inserted in the cathode lead to provideadequate grid biasing potential in a manner well known. This arrangementfor producing grid bias can of course be replaced by any known method.Items 38 and 39 represent the voltage divider corresponding to items l9and 20 or 2| and 2| in Figures 4 and 5 and may consist of any desiredimpedance elements as is understood from the above. The valve 25 can beof any type such as a multi-grid of the screen grid valve or pentodetype, or it may be constituted by one of the elec trode systems of adouble or multiple purpose valve.

Figure 7 shows an arrangement of the latter type. Here a double triode40 has one triode system (the upper section in the figure) whichperforms the function of the valve 25 of Figure 6 and another (the lowersection) which performs the function of the valve 3| of Figure 6. Thereare shown several minor modifications in Figure 7 over Figure 6. Thejunction point of the voltage divider 38, 39 is connected to the grid ofthe phase reversing (lower) triode section of valve 49 through acoupling condenser 4| and the grid of this section is biased by aseparate biasing source 42 connected in series with the grid leak 35.Items 43, 44 and 45 represent a coupling condenser, grid leak andbiasing source for the upper or input triode section of the valve 40,while items 46 and 41 are grid leak resistances for the push-pull valves28 and 29, respectively, the output of which is combined by means of atransformer 48 with a center tapped primary connected to ground orcathode through the high tension source 48 in a manner well known.Valves 28 and 29 may be indirectly heated valves in place of thedirectly heated type shown. Item 50 is a common grid biasing source forthe valves 28 and 29 arranged in a known manner.

Another application of circuits as shown in Figures 6 and 7 is theproduction from an oscillatory voltage source having two terminals, oneof which is connected to earth of a symmetrical control voltage forapplication to a pair of deflecting plates of a cathode ray tube such asa television reproducer type. A further application of a circuit inaccordance with the invention is in place of a transformer arrangementof the push-pull type for coupling a two-wire line, one. wire of whichis earthed, such as a concentric high frequency cable, to a two-wireline, the conductors of which are to be symmetrical to earth. Thecircuits of this invention are particularly to be recommended in thosecases where owing to the wide range of frequencies to be transmitted,such as in the case of television signals, the usual transformerarrangements are not satisfactory or convenient.

Figure 8 shows a modification wherein the potential on the datumterminal b, in relation to which the input voltage on the terminal a aswell as the output voltage on the terminal 0 are measured, can be put atany desired potential in relation to earth potential. For example, if120 be a variable potential on the terminal b in relation.

to earth (terminals e and f) and v1=vo+u, the corresponding potential onthe terminal a, then the potential 1:: on the terminal 0 is equal tovu-u. As will be obvious from the figure, the sum voltage vo+u will beset up between the terminals g and f and the diiference voltage oo-uwill occur between the terminals 0 and 1. on may, for example, be amodulating frequency alternating voltage, and u a high frequency carrierwave voltage which is to be modulated in accordance with on. From thesum and difierence voltages between the terminals 0 and g, respectively,and earth, a modulated frequency 0 can be derived at terminals h, j bymeans of a push-pull modulation circuit as shown, in-which 5| and 52 areresistancesand 53 and 54 rectifiers which may be of any type, such asdiodes or thermionic valves. Here again there is the advantage ofelimination of transformers which, especially Where the frequency rangeinvolved is wide, tend to be expensive and to introduce distortion.

As will be evident from the above, the invention is not limited to thespecific circuits and methods disclosed and described herein forillustration and the underlying principle and inventive concept aresusceptible of numerous variations and modifications differing from theembodiments illustrated and coming within the broader scope and spiritof the invention as defined in the appended claims. The speciflcationand drawings are intended accordingly to be regarded in an illustrativerather than a limiting sense.

I claim:

1. A four-pole network having an input and an output, a potentialdivider connected between an input terminal and an output terminal ofsaid network so as to be in series relation with both said input andoutput, an electron discharge device having at least a cathode, a gridand an anode, a coupling connection from an intermediate point of saidpotential divider to said grid, a connection from said anode to saidoutput terminal, and a further connection from said cathode to both theremaining input and output terminals of said network.

2. A four-pole network having an input and an output, a potentialdivider connected between an input terminal and an output terminal ofsaid network so as to be in series relation with both said input andoutput, an electron discharge device having at least a cathode, a gridand an anode, a coupling connection from an intermediate point of saidpotential divider to said grid, a load impedance and a high potentialsource in the anode circuit of said device, a capacitative connectionfrom said anode to said output terminal, and a connection from saidcathode to both the remaining output and input terminals of saidnetwork.

3. A four-pole network having an input and an output, a potentialdivider connected in series between an input and an output terminal ofsaid network, an electron discharge device having at least a cathode, agrid and an anode, a coupling connection from an intermediate point ofsaid potential divider to said grid, a load impedance and a highpotential supply source in the anode circuit of said device, aconductive connection between the anode and said output terminalincluding a further high potential source connected in opposition tosaid first source, and a connecohmic resistance and said intermediatepoint forms approximately the center thereof.

6. In a network as claimed in claim 1, wherein said potential dividerconsists of a high ohmic inductance and said intermediate point is atapproximately the center thereof.

7. A four-pole network having an input and an output, a potentialdivider connected in series between an input terminal and an outputterminal of said network, an electron discharge device having at least acathode, a grid and an anode, a coupling connection from an intermediatepoint of said potential divider to said grid, a connection from saidanode to said output terminal, and a further connection from saidcathode to both the remaining input and output terminals of saidnetwork, said intermediate point being chosen in respect to theconstants of the remaining circuit elements such that the phase of theoutput potential of said network is shifted by substantially 180' withrespect to the phase of the impressed input potential and that theamplitude of the output potential is substantially independent ofamplification constant of said valve.

8. A phase reversing system comprising an electron valve having an inputand an output,

means for impressing a potential upon said input,

means for deriving a corresponding potential of reversed phase from saidoutput, and means for substantially suppressing the eflect of theampliilcation of said valve.

9. A: phase reversing system comprising an electron valve having aninput and an output, means for impressing a potential upon said input,means for deriving a corresponding potential of reversed phase from saidoutput, and inverse teedback means for substantially suppressing theeffect of the amplification of said valve.

GUSTAV GUANELLA.

